Evolution of locomotion in slug caterpillars (Lepidoptera: Zygaenoidea: limacodid group)

Larval locomotion of species in the limacodid-group families Limacodidae, Dalceridae, Megalopygidae, Aididae, and Somabrachyidae is described in phylogenetic context.Function of structures involved in locomotion reported include thoracic legs, abdominal prolegs or suckers, and spinnerets.Additional segments with prolegs or suckers in the limacodid-group families increase their ventral surface contact with the substrate.The limacodid + dalcerid clade has the most fluid waves of locomotion because of a highly flexible ventrum, tactile lateral setae and size reduction of prolegs and thoracic legs.On flat surfaces aidids have a similar locomotion to limacodids due to short prolegs and smooth lateral and subventral warts, which contact the substrate, whereas in megalopygids the motion of each proleg segment is more apparent because contact of the substrate is primarily with membranous pads on their prolegs.Ventral adhesion in the limacodid + dalcerid clade is increased by the spinneret both in laying down wet silk and in cleaning debris off the ventrum.Evolution of locomotion and its adaptive significance in the limacodid group are discussed.